<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div id="box">this is <b>box</b></div>
    <script>
      const box = document.getElementById("box");

      // console.log(box.hidden); //false
      // setTimeout(() => {
      //   box.hidden = true;
      //   console.log(box.hidden); //true
      // }, 4000);

      setInterval(() => {
        box.hidden = !box.hidden;
      }, 1000);
    </script>
  </body>
</html>
